Power exhaust studies in the Divertor Tokamak Test facility

Dealing with power exhaust is one of the most difficulty tasks in foreseen fusion reactor based on magnetic confinement. Itis commonly recognized that the standard Single Null Divertor (SND) configuration can face some difficulties in providing ascalable solution based on H-mode tokamak operation compatible with present solid divertor target technological solutions.To provide a safer solution two approaches are being considered: the adoption of alternative divertor magnetic configurations (ADCs) could favour plasma detached operations, thus mitigating the heat load on targets; liquid metallictargets are also studied for their ability to survive to high heat load while providing also a self-mitigation of incoming heatflux.The Divertor Test Tokamak (DTT) facility [1] is being designed to specifically explore and qualify most of the ADCs (andliquid metal targets) with divertor conditions as close as possible to those foreseen in DEMO fusion reactor in terms ofpower crossing the separatrix, Psep/R, and heat flux decay length, ?q. All of the present more promising alternative divertorconfigurations are realizable in DTT: the flux flaring towards the target (X divertor), the increasing of the outer target radius(Super-X) and the movement of a secondary x-point inside the vessel (X-point target) as well as the entire range ofSnowflake (SFD+/SFD-) configurations [2] and the presently reconsidered double null (DND) one. This divertorconfigurations flexibility is supplemented by a similar flexibility in operation scenarios which for example allows scanningtriangularity from the DEMO positive value to negative one or moving from H-mode to the I-mode to test possible ELMs freehigh confinement regimes.To analyse the possible beneficial effects ADCs configuration in DTT and starting to optimize plasma scenario and divertorgeometry, 2D edge fluid-kinetic simulations has been done on previously described divertor configurations. The analysishas shown in pure deuterium the extension of the detached operation towards higher Psol power with all the ADCs, withrespect to the SND, with the best results achieved at all targets for the SFD-. Modelling has also shown that the ADCsadvantages extend to the case of (Ne/Ar) impurity seeding, whereby detached operations can be reached with a lower Zeffor dilution at the separatrix compared to the SND.